Preferential invasion of malarial merozoites into young red blood cells

The preferential invasion of malarial merozoites into subpopulations of red blood cells (RBCs) in vivo and in vitro has been the subject of repeated discussions. In this paper, an attempt is made to summarize these discussions and to pinpoint the mechanism by which this preference could arise. The available data suggest that a relatively simple mechanism, related to the capability of the merozoite to rearrange the proteins of the cytoskeleton of the RBC may determine the invasion rate into mature versus very young RBCs (reticulocytes). There is no evidence for significant differences between mature RBCs and reticulocytes in the presence of membrane proteins which might play a role in receptor-ligand binding of merozoites to their host cell. Consequently, the concept of "reticulocyte preference" is left and the ability of penetrating both mature and immature RBCs, versus immature RBCs only, is given as an explanation for the presence of ringforms exclusively in reticulocytes as observed for several species of vivax-type malaria parasites. The possible consequences of preferential invasion for the infection (in vivo) and the culture (in vitro) of different plasmodial species are discussed.